1. Technical Field
The present invention pertains to wireless networks employing voice reservation protocols. In particular, the present invention pertains to multi-hop wireless Ad-Hoc networks employing voice reservation with dynamic selection of frame architectures depending on voice mode operation (e.g., simplex/duplex) and associated retransmission/acknowledgement mechanisms.
2. Discussion of the Related Art
Wireless Ad-Hoc networks may transfer information in the form of voice and data. However, transfer of voice information within such networks has more stringent requirements relative to those for data transfer since voice information is transferred as a continuous stream of packets with each packet representing a frame of voice data that has to be received in correct time order. If a frame is received late, the frame is considered lost. In a tactical environment, an acceptable delay is typically required to be on the order of 50 ms/hop (e.g., milliseconds per hop) with a completion rate in the approximate range of 95% to 99%.
Time Division Multiple Access (TDMA) is a scheme that allows plural users to share the same communication media. The TDMA frame may be utilized for integration of voice and data, where the TDMA frame is divided between voice and data, while still sharing the same channel. Basically, each TDMA frame is partitioned into a quantity of time slots within which information (e.g., voice and/or data) may be transferred over the communication media between network sites. Plural users may reserve (or be assigned) different time slots within the TDMA frame to perform communications over the same communication media. The use of a TDMA architecture and a conventional Packet Reservation Multiple Access (PRMA) scheme was first proposed for voice communication between a base station and a mobile user. However, PRMA may further be applied for home networking technologies.
The key feature of PRMA is that a time slot is reserved by a user through an uplink and is later confirmed by the base station through a down link. However, users have to contend for any unused time slots in order to get a reservation. The original PRMA scheme allows plural users to contend for time slot reservation and suffer the consequence of collisions (e.g., plural transmissions on the same time slots for reservations). The PRMA scheme was later refined by inserting dedicated reservation time slots in the TDMA frame. Plural users utilize these dedicated time slots by using conventional protocols (e.g., ALOHA, CSMA, etc.) to make time slot reservations.
In the original PRMA scheme, a user intending to send voice information uses an available time slot to inform the base station of a reservation. In a tactical environment, the base station does not exist. Therefore, the reservation must be set up through a signaling protocol. One conventional signaling protocol is RSVP which conveys the application resource requirements to the network. The reservation in this protocol is receiver oriented. Typically, the source network site or sender transmits a path message down stream to the receiver which returns a reservation request (RESV) message up stream to the sender. The RESV message travels hop by hop from the receiver to the source. The resources are allocated in response to intermediate routers determining availability of sufficient resources to satisfy the request.
The related art described above suffers from several disadvantages. In particular, the techniques described above concern either cellular networks or home networks. The cellular network is a one-hop network (e.g., between the base station and the mobile user), while the home network consists of a down-link and up-link similar to the cellular network infrastructure. Thus, these techniques are limited to specific types of networks and do not address the environments of Ad-Hoc multi-hop networks. With respect to multi-hop packet radio networks, there are protocols dealing with a distributed time-slot assignment. However, this application is primarily limited to data transfer. Although the enhanced PRMA scheme employs dedicated time slots for reservations, the resources available in the TDMA frame for voice information are reduced, while controlling the number of time slots required for a successful time slot reservation is difficult and complex.
Basically, if time slots can be successfully reserved, collision-free voice communication can be maintained. However, the techniques described above generally do not address the issue of packet loss due to external interference. In a tactical environment, interference could be due to unfriendly jamming. Although spread spectrum technology can provide some resistance, packet loss may still occur depending on the number and strength of the interference sources.
In a home environment, interference may originate from a microwave oven. Although the conventional HomeRF architecture addresses packet loss due to external interference, this architecture is simplified and limited due to the one-hop nature of the home network.
In addition, the RSVP protocol is receiver oriented, where the reservation is made only on the reverse path. Further, with respect to TDMA slot reservation, each network node cannot independently make slot reservations since the slot reservation of one node depends upon the reservation of the previous nodes.